3D printing technology is the ability for anyone with a printer, material and a modeling app to render objects into three-dimensions, as opposed to normal printing, which deals with two.
In this case, actual objects are created, using whatever materials the printer is equipped to handle. In lay terms, types of plastics are primarily used in the consumer editions, but various things could be used, from metals to genetic material, given the right processes, software and hardware to do it.
So far, the technology has not had a great impact on our daily lives, but that could change if consumer price points were to come down, as long as material costs. For that to happen usually requires mass adoption of some kind, and so far, outside of promising manufacturing, industrial, medical and other mass production processes, the technology has yet to make its way into many homes.
How it could change our lives is in numerous ways. For those who might be familiar with some versions of Star Trek, there was a device called a replicator that primarily was known for creating whatever food or beverage the person wanted. The replicator's database had to have the food/beverage inputed, but once that was taken care of, the machine could not only create the ingredients and apply them properly, but also the serving dishes.
While no where near to that yet, 3D printing could allow us to replace worn out car parts with a functional replica. There are medical professionals who hope to one day print out tissue to repair damaged organs, if not flat out replace them. Just like the replicator, a restaurant could conceivably give a 3D printer the plans for a hamburger and then let it put it together.
As mentioned above, the main issues are initial costs, ongoing costs, and use. If a high quality, versatile 3D printer can drop below $500 USD and create say, kitchenware out of normal materials (not just plastic, but glass, etc.), while the material cost is kept to a minimum, there might be a market. Instead of running to the store to try to replace a broken tea cup, the printer could do it.
It's more likely that the main adoption will take place on the manufacturing and commercial levels, which could be a part of the robotic/AI revolution that is expected to take place within a short period of time.